Lawn Mower Blowing Oil Out Exhaust (Fixing Briggs & Stratton Issue)

The relentless hum of a lawn mower on a summer afternoon is a sound many of us associate with well-kept lawns and suburban bliss. But that idyllic scene can quickly turn sour when your trusty Briggs & Stratton engine starts spewing oil out of the exhaust. It’s a common problem, yet often misunderstood. From my years spent not just tending my own property but also advising neighbors and friends, I’ve seen firsthand the frustration this issue causes. What starts as a simple maintenance task can quickly escalate into a mechanical mystery. We’re not just talking about a messy situation here; we’re talking about potential engine damage and unnecessary expenses.

Understanding the Issue: Why is My Lawn Mower Spewing Oil?

Before we dive into the repair process, it’s crucial to understand the underlying reasons why your lawn mower is blowing oil. It’s not just a random occurrence; it’s a symptom of an underlying problem within the engine.

The Basics of a Briggs & Stratton Engine

Briggs & Stratton engines, commonly found in lawn mowers, operate on a four-stroke cycle: intake, compression, combustion, and exhaust. Oil plays a vital role in lubricating the engine’s internal components, reducing friction, and dissipating heat. The oil is contained within the crankcase and should never enter the combustion chamber. When oil does find its way into the combustion chamber, it gets burned along with the fuel, resulting in blue or white smoke emitting from the exhaust.

Common Causes of Oil in the Exhaust

Here are the most frequent culprits behind oil escaping through the exhaust:

Overfilling the Oil: This is perhaps the most common mistake. Adding too much oil to the crankcase can cause it to splash onto the piston and cylinder walls, leading to it being burned during combustion. I’ve seen this happen countless times, especially after someone performs an oil change and isn’t careful with the measurements.
Tipping the Mower: Tipping the mower on its side, particularly with the carburetor facing downwards, can cause oil to flow into the cylinder. This is a frequent issue when cleaning the mower deck or performing maintenance. I learned this the hard way when I first started maintaining my lawn. I tipped it over to clean the underside, and the next time I started it, a plume of smoke filled my yard.
Worn Piston Rings: Piston rings seal the combustion chamber and prevent oil from entering. Over time, these rings can wear down, creating gaps that allow oil to seep into the combustion chamber. This is more common in older mowers or those that haven’t been properly maintained.
Damaged Cylinder: Scratches or damage to the cylinder wall can also create pathways for oil to enter the combustion chamber. This can be caused by debris entering the engine or by running the engine without sufficient lubrication.
Faulty Valve Seals: Valve seals prevent oil from leaking down the valve stems and into the combustion chamber. If these seals are damaged or worn, oil can leak into the cylinder and be burned.
Crankcase Breather Problems: The crankcase breather regulates pressure within the crankcase. If it’s clogged or malfunctioning, it can cause pressure to build up, forcing oil past the piston rings and into the combustion chamber.

Diagnosing the Problem: A Step-by-Step Approach

Before you start tearing apart your engine, it’s essential to accurately diagnose the cause of the oil leak. Here’s a systematic approach I use to pinpoint the problem:

Step 1: Check the Oil Level

The first and easiest step is to check the oil level. Use the dipstick to ensure the oil is not overfilled. If it is, carefully drain the excess oil until it reaches the proper level. Remember to consult your owner’s manual for the correct oil capacity.

Step 2: Inspect for External Leaks

Examine the engine for any visible oil leaks. Pay close attention to the areas around the oil seals, gaskets, and the oil drain plug. Clean the engine thoroughly and run it for a few minutes to see if you can spot any fresh leaks. Sometimes, a loose drain plug or a cracked gasket is all that’s causing the problem.

Step 3: Observe the Exhaust Smoke

The color of the exhaust smoke can provide clues about the problem. Blue or white smoke indicates that oil is being burned in the combustion chamber. Black smoke, on the other hand, usually indicates a fuel mixture issue. Note when the smoke is most prevalent – is it at startup, during operation, or both? This can help narrow down the source of the oil leak.

Step 4: Perform a Compression Test

A compression test measures the pressure within the cylinder. Low compression can indicate worn piston rings, a damaged cylinder, or leaky valves. You’ll need a compression tester for this step. Follow the instructions that come with the tester and compare the results to the specifications in your engine’s service manual. A significant difference between cylinders can indicate a problem with one or more of the cylinders.

Step 5: Check the Crankcase Breather

The crankcase breather is usually located on the side of the engine. Remove it and inspect it for any clogs or damage. A common issue is a foam filter that becomes saturated with oil and restricts airflow. Clean or replace the breather if necessary.

Step 6: Cylinder Leak-Down Test (Advanced)

If the compression test reveals low compression, a cylinder leak-down test can help pinpoint the source of the leak. This test involves pressurizing the cylinder with compressed air and listening for leaks coming from the exhaust, carburetor, or crankcase. Air leaking from the exhaust indicates a leaky exhaust valve, air leaking from the carburetor indicates a leaky intake valve, and air leaking from the crankcase indicates worn piston rings or a damaged cylinder.

Fixing the Problem: Step-by-Step Solutions

Once you’ve diagnosed the cause of the oil leak, you can move on to the repair process. Here are some common solutions for the issues we discussed earlier:

Solution 1: Correct Oil Level

If the oil level is too high, simply drain the excess oil using the oil drain plug or a siphon. Use a measuring container to ensure you drain the correct amount. Always refer to your owner’s manual for the correct oil capacity. After adjusting the oil level, run the mower for a few minutes and see if the smoking stops.

Solution 2: Prevent Tipping

Avoid tipping the mower on its side, especially with the carburetor facing downwards. If you need to clean the mower deck, use a scraper or a pressure washer instead. Alternatively, invest in a mower lift, which allows you to safely lift the mower without tipping it.

Solution 3: Replace Worn Piston Rings

Replacing piston rings is a more involved repair that requires disassembling the engine. This is a common repair for older mowers with high hours. Here’s a general overview of the process:

Disassemble the Engine: Remove the engine from the mower deck and disassemble it, following the instructions in your service manual. Pay close attention to the order of the parts and take photos as you go to help with reassembly.
Remove the Piston: Carefully remove the piston from the cylinder. You may need a piston ring compressor to do this without damaging the piston or cylinder.
Remove the Old Rings: Use a piston ring expander tool to remove the old piston rings.
Clean the Piston: Clean the piston thoroughly, removing any carbon deposits or debris.
Install the New Rings: Install the new piston rings using the piston ring expander tool. Make sure the ring gaps are staggered according to the service manual’s specifications.
Reassemble the Engine: Reinstall the piston into the cylinder, using a piston ring compressor. Reassemble the engine, following the reverse order of disassembly.
Refill with Oil: Refill the engine with the correct amount of oil.
Test the Engine: Start the engine and check for any leaks or smoke.

This is a challenging repair, so if you’re not comfortable working on engines, it’s best to take it to a qualified mechanic.

Solution 4: Repair Damaged Cylinder

If the cylinder is scratched or damaged, it may need to be honed or re-bored. Honing involves using a specialized tool to smooth out the cylinder walls. Re-boring involves enlarging the cylinder to remove the damaged area. Both of these procedures require specialized equipment and expertise, so it’s best to take the engine to a machine shop.

If the damage is severe, the cylinder may need to be replaced altogether. This is a more expensive option, but it may be necessary if the cylinder is beyond repair.

Solution 5: Replace Faulty Valve Seals

Replacing valve seals also requires disassembling the engine. Here’s a general overview of the process:

Remove the Cylinder Head: Remove the cylinder head from the engine.
Compress the Valve Springs: Use a valve spring compressor to compress the valve springs and remove the valve keepers.
Remove the Valves: Remove the valves from the cylinder head.
Remove the Old Seals: Use a valve seal removal tool to remove the old valve seals.
Install the New Seals: Install the new valve seals using a valve seal installation tool.
Reinstall the Valves: Reinstall the valves into the cylinder head.
Reinstall the Valve Keepers: Reinstall the valve keepers, using the valve spring compressor.
Reinstall the Cylinder Head: Reinstall the cylinder head onto the engine.
Adjust the Valves: Adjust the valves according to the service manual’s specifications.
Test the Engine: Start the engine and check for any leaks or smoke.

This is another challenging repair, so it’s best to take it to a qualified mechanic if you’re not comfortable working on engines.

Solution 6: Clean or Replace Crankcase Breather

Remove the crankcase breather and inspect it for any clogs or damage. Clean the breather with a solvent or replace it if necessary. Make sure the breather is properly installed and that all the hoses are connected correctly.

Preventive Maintenance: Keeping Your Lawn Mower Healthy

Preventive maintenance is key to avoiding oil leaks and other engine problems. Here are some tips to keep your lawn mower running smoothly:

Change the Oil Regularly: Change the oil according to the manufacturer’s recommendations. This is typically every 25-50 hours of operation. Regular oil changes keep the engine lubricated and prevent wear and tear. I always mark the date of my last oil change on a sticker and attach it to the engine as a reminder.
Use the Correct Oil Type: Use the correct oil type and viscosity for your engine. Refer to your owner’s manual for the recommended oil specifications. Using the wrong oil can damage the engine and lead to oil leaks.
Clean the Air Filter Regularly: A dirty air filter can restrict airflow to the engine, causing it to run rich and produce more exhaust smoke. Clean or replace the air filter regularly, depending on the conditions in which you operate the mower.
Sharpen the Blades Regularly: Sharp blades make it easier for the mower to cut grass, reducing the strain on the engine. Sharpen the blades every 25 hours of operation or as needed.
Store the Mower Properly: Store the mower in a dry place and protect it from the elements. Drain the fuel tank before storing the mower for extended periods to prevent fuel from going bad.
Inspect Regularly: Make it a habit to inspect your mower regularly for any signs of wear and tear, such as loose bolts, cracked hoses, or worn belts. Addressing these issues early can prevent more serious problems down the road.

Real-World Examples and Case Studies

Let me share a couple of real-world examples from my own experience that highlight the importance of proper diagnosis and maintenance:

Case Study 1: The Overfilled Oil Catastrophe

A neighbor of mine, let’s call him Tom, was having trouble with his lawn mower. It was blowing oil out of the exhaust and running rough. Tom, being a resourceful guy, decided to tackle the problem himself. He started by changing the oil, but he accidentally overfilled it. The next time he started the mower, it spewed out a cloud of blue smoke.

I went over to help him, and after checking the oil level, we realized the problem. We drained the excess oil, and the smoking stopped immediately. This simple mistake could have been avoided by simply following the instructions in the owner’s manual and being careful with the oil measurements.

Case Study 2: The Worn Piston Ring Mystery

Another friend, Sarah, had an older lawn mower that was blowing oil out of the exhaust. She had tried changing the oil and cleaning the air filter, but the problem persisted. After performing a compression test, we discovered that the compression was low in one of the cylinders. This indicated that the piston rings were likely worn.

Sarah decided to take the mower to a mechanic, who confirmed our diagnosis. The mechanic replaced the piston rings, and the mower ran like new again. This case highlights the importance of proper diagnosis and the need for more involved repairs in some cases.

Cost-Benefit Analysis: DIY vs. Professional Repair

When faced with a lawn mower blowing oil out of the exhaust, you have two main options: tackle the repair yourself or take it to a professional mechanic. Here’s a cost-benefit analysis to help you decide which option is best for you:

DIY Repair

Pros:

Lower Cost: DIY repairs are typically cheaper than professional repairs, as you only have to pay for the parts.
Learning Experience: DIY repairs can be a valuable learning experience, allowing you to gain a better understanding of how your lawn mower works.
Flexibility: You can work on the repair at your own pace and on your own schedule.

Cons:

Time Commitment: DIY repairs can take a significant amount of time, especially if you’re not familiar with engine repair.
Potential for Mistakes: There’s always a risk of making mistakes during a DIY repair, which can lead to further damage to the engine.
Tool Requirements: Some repairs require specialized tools, which you may not have on hand.

Professional Repair

Pros:

Expertise: Professional mechanics have the knowledge and experience to diagnose and repair lawn mower problems quickly and efficiently.
Warranty: Professional repairs often come with a warranty, which protects you against further problems.
Convenience: You don’t have to spend your time and effort on the repair.

Cons:

Higher Cost: Professional repairs are typically more expensive than DIY repairs.
Scheduling: You may have to wait for an appointment with a mechanic.
Lack of Control: You have less control over the repair process.

Ultimately, the decision of whether to DIY or hire a professional depends on your skills, experience, and budget. If you’re comfortable working on engines and have the necessary tools, a DIY repair can be a cost-effective option. However, if you’re not confident in your abilities or if the repair is complex, it’s best to take it to a professional.

Firewood Preparation: A Tangential Tip

While we’re on the subject of engines and outdoor maintenance, let me share a tip related to firewood preparation. Many people use gasoline-powered log splitters to make firewood. Just like lawn mowers, these engines require regular maintenance to run smoothly. Always check the oil level before each use, and change the oil according to the manufacturer’s recommendations. Also, be sure to use fresh fuel and store the splitter properly when not in use. A well-maintained log splitter will make firewood preparation much easier and more efficient.

Wood Science and Fuel Value

Understanding the science behind firewood can also help optimize your wood-burning experience. Different types of wood have different fuel values, measured in BTUs (British Thermal Units) per cord. Hardwoods, such as oak, maple, and ash, have higher BTU values than softwoods, such as pine and fir. This means that hardwoods produce more heat and burn longer than softwoods.

The moisture content of firewood is also crucial. Freshly cut wood can have a moisture content of 50% or more, which significantly reduces its fuel value and makes it difficult to burn. Properly seasoned firewood should have a moisture content of 20% or less. Seasoning involves stacking the wood in a well-ventilated area for at least six months, allowing it to dry out.

To measure the moisture content of firewood, you can use a moisture meter. Simply insert the probes of the meter into the wood, and it will display the moisture content as a percentage. This is a valuable tool for ensuring that your firewood is properly seasoned and ready to burn.

Conclusion: Taking Control of Your Lawn Mower’s Health

Dealing with a lawn mower blowing oil out of the exhaust can be frustrating, but with a systematic approach and a little bit of knowledge, you can diagnose and fix the problem yourself. Remember to start with the simple solutions, such as checking the oil level and preventing tipping. If the problem persists, perform a compression test and check the crankcase breather. If necessary, consider replacing the piston rings or valve seals.

Preventive maintenance is key to avoiding oil leaks and other engine problems. Change the oil regularly, use the correct oil type, clean the air filter, and store the mower properly. By following these tips, you can keep your lawn mower running smoothly for years to come.

And remember, if you’re not comfortable working on engines, don’t hesitate to take it to a qualified mechanic. It’s better to spend a little money on professional repair than to risk further damage to your engine.

Now that you have a better understanding of the causes and solutions for a lawn mower blowing oil out of the exhaust, you can tackle this problem with confidence. Get out there, get your hands dirty, and get your mower back up and running!